It is required in various industries to dispense granular product from a tank or container into pressurized environment, such as the transfer conduit of a pneumatic conveyor. For example in the agriculture industry, air seeders are well known for seeding crops and typically comprise a frame with furrow openers mounted thereon that are configured to create furrows in a field surface. Tanks mounted on a cart or on the frame contain agricultural products such as seeds, chemicals, and fertilizers and metering devices dispense agricultural products from each tank into a distribution network connected between the tanks and the furrow openers. A fan creates an air stream flowing through the distribution network to carry the agricultural products from the tanks to the furrow openers.
The distribution network commonly includes one or more larger primary conduits from the tanks to the frame, which are each connected to the input port of a manifold which receives the air stream and divides and directs the air stream, and the agricultural products entrained in the air stream, through output ports into a number of smaller secondary conduits. The secondary conduits carry the air stream and products downstream either to another manifold for further division, or to the furrow openers. In some distribution networks conduits are connected directly from the furrow openers to the metering devices, and no secondary division of the air stream is needed.
Most modern air seeders have furrow openers that deliver seed to seed furrows and fertilizer to separate fertilizer furrows. These may be totally separate furrow openers mounted on separate shanks, such as mid row fertilizer banding furrow openers which are remote from the seed furrow openers, or combination furrow opener where a single shank supports a furrow opening tool that makes one furrow for seed and a separate furrow for fertilizer. There are also commonly two separate distribution networks, one delivering product from selected ones of the tanks to the seed furrows, and one delivering product from selected ones of the tanks to the fertilizer furrows. In this application the terms “seed” and “fertilizer” are not meant literally or in a limiting fashion, since in many cases some fertilizer is metered into the air stream carrying the seed, and also in some instances it may be that fertilizer may be directed into the “seed” furrows, and vice versa if conditions warrant it. The terms “seed” and “fertilizer” are simply convenient to differentiate the two separate distribution networks or air streams. In an air seeder it is generally desirable to be able to direct agricultural product from any of the tanks into any of the available air streams.
One typical type of seed metering device includes a rotating feed roller with recesses that can be in the form of grooves extending longitudinally along the length of the outer surface of roller parallel to the axis of rotation, or in the form of notches or pockets or the like spaced evenly along the outer surface of the roller. The feed roller is typically mounted below the feed opening at the bottom of a product tank and configured such that the intake side of the roller is inside the feed opening exposed to the seeds in the tank and the outer output side is above the air stream that carries the seeds to the furrow openers to be deposited in the ground. As the roller rotates, granules of the agricultural product being dispensed fill the recesses and are carried from the seed tank and fed into the air stream.
Instead of a feed roller some metering devices use an auger with an input end under the tank and an output end oriented to dispense product into the air stream. Again the metering rate is proportional to the speed of auger rotation. The number of seeds dispensed is proportional to the rotational speed of the feed roller or auger, and the rate of metering seeds is adjusted by varying the rotational speed. The rotational speed is also coordinated with ground speed so that the same amount of seed is dispensed for each foot of distance travelled. Ground speed correlation can be achieved by using a ground drive, or as is common in modern air seeders, the ground speed is sensed and the meters are driven by motors where the speed is adjusted to correspond to the ground speed.
The size of the granules of the agricultural products metered varies significantly, and the application rate of the various products also varies significantly from as low as about three pounds per acre to 300 pounds per acre or more. While the metering devices can typically be adjusted to provide a significant range of metering rates for different sized products, when changing from a very high rate to a very low rate, or from a large to a small granule size, many metering devices require that the feed roller or auger be changed to provide a steady and even stream of product for uniform application across the field surface.
The intake side of the metering device is exposed to whatever the air pressure is inside the tank, while the output side is exposed to the increased air pressure of the air stream. A pressure differential across the metering device between the tank and the air stream can cause air to flow back through the meter from the higher pressure side to the lower pressure side as the product is being metered into the air stream, disrupting the flow. It has been known to seal the metering device to provide an air lock between the meter and the pressurized distribution tube however such air lock systems have been costly and problematic and present air seeders typically provide a conduit connecting the air stream at the output end of the metering device to the top of the interior of the tank to pressurize the tank so that there is no pressure differential across the metering. This requires that the tank be sealed during operation and designed to resist deformation due to forces exerted by the pressure. The resulting restricted tank shapes, and small fill openings are challenging for operators to use, such as when aligning the fill opening with a fill conveyor, and also restrict the volumes capable of being held in a defined space/foot print.
The gravity feed aspect of the metering devices also creates some compromises. The tanks and their mounting structures are required to be of sufficient height to allow metering devices and drives to function directly underneath. Any maintenance, metering component changes or associated operations require operators to crawl under the unit and work off the ground.